Department of Diagnostic and Interventional Radiology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
J Thorac Imaging. 2012 Mar;27(2):113-20. doi: 10.1097/RTI.0b013e31820b8696.
To evaluate the impact of dose reduction in multidetector computed tomography pulmonary angiography (CTPA) for detection of pulmonary embolism (PE).
After induction of PE in 6 anesthetized pigs, a 64-detector-row CTPA was performed at 3 different dose protocols: A (120 kV/120 mAseff.), B (120 kV/80 mAseff.), and C (80 kV/80 mAseff.). Images were evaluated by 2 radiologists independently. A high-dose CTPA (120 kV/250 mAseff.) served as a reference standard. Sensitivity, specificity, and positive and negative predictive values were calculated and compared using the Wilcoxon test. Interobserver agreement was determined by calculation of κ values. Radiation exposure and objective image parameters were assessed and compared with a 2-sided t test.
In the reference scan, a total of 94 emboli were detected: 17 in the main and lobar pulmonary level (category A), 47 in the segmental level (category B), and 30 in the subsegmental level (category C). All protocols reached high diagnostic accuracy in the detection of PE in category A. No significant difference was observed between protocols A and B in the detection rate of segmental and subsegmental PE (sensitivity: 93.6% and 91.5% vs 85.1% and 87.2%; positive predictive value: 100% and 97.7% vs 97.5% and 95.3%). Interobserver agreement was excellent at the segmental (κ=0.97 and 0.94) and subsegmental levels (κ=0.94 and 0.92). Using protocol C, the detection rate of segmental and subsegmental emboli was significantly impaired and interobserver agreement was significantly inferior (sensitivity: 46.8% and 44.6% at segmental and 56.7% and 50.0% at subsegmental level; κ=0.70 and 0.60, respectively; P<0.05). Vessel attenuation was significantly higher in protocol C, [710.3 Hounsfield units (HU) ±200.6 SD] than in protocols A (414.4 HU±82.5 SD) and B (428.8 HU±78.9 SD) (P<0.001). Signal-to-noise and contrast-to-noise ratios were significantly decreased in protocols B (55.6; 45.8) and C (44.3; 39.4) compared with protocol A (62.1; 52.3) (P<0.05). Radiation dose was significantly reduced between protocols A and B and protocols B and C [volume CT dose index (CTDIvol): 7.1 vs 4.7 vs 1.4 mGy; dose-length product: 199.5 vs 132.1 vs 39.4 mGy·cm and E: 3.39 vs 2.25 vs 0.6 mSv; P<0.05].
This animal study proves the diagnostic use of a low-dose CTPA protocol with 80 mAseff. at 120 kV for PE evaluation without significant loss of diagnostic accuracy compared with a standard protocol with 120 mAseff. Using an "ultra-low"-dose CTPA protocol (80 kV; 80 mAseff.), emboli detection at the segmental and subsegmental level is significantly impaired, whereas evaluation of central emboli is still feasible with high diagnostic accuracy.
评估减少多排螺旋 CT 肺动脉造影（CTPA）剂量对肺栓塞（PE）检测的影响。
在 6 只麻醉猪中诱发 PE 后，分别在 3 种不同剂量方案（A：120 kV/120 mAs 有效剂量；B：120 kV/80 mAs 有效剂量；C：80 kV/80 mAs 有效剂量）下进行 64 排螺旋 CTPA。由 2 位放射科医生独立评估图像。高剂量 CTPA（120 kV/250 mAs 有效剂量）作为参考标准。使用 Wilcoxon 检验计算并比较敏感性、特异性、阳性和阴性预测值。通过计算 κ 值来确定观察者间的一致性。使用双侧 t 检验评估并比较辐射暴露和客观图像参数。
在参考扫描中，共发现 94 个栓塞物：主肺动脉和叶肺动脉水平（A 类）17 个，段肺动脉水平（B 类）47 个，亚段肺动脉水平（C 类）30 个。所有方案在检测 A 类 PE 时均达到了较高的诊断准确性。在检测段和亚段 PE 的检出率方面，方案 A 和 B 之间没有显著差异（敏感性：93.6%和 91.5% vs 85.1%和 87.2%；阳性预测值：100%和 97.7% vs 97.5%和 95.3%）。在段和亚段水平，观察者间的一致性非常好（κ 值为 0.97 和 0.94）。使用方案 C，段和亚段栓塞物的检出率显著降低，观察者间的一致性显著降低（敏感性：段水平为 46.8%和 44.6%，亚段水平为 56.7%和 50.0%；κ 值分别为 0.70 和 0.60；P<0.05）。方案 C 中的血管衰减值显著高于方案 A [710.3 亨氏单位（HU）±200.6 标准差]和方案 B [414.4 HU±82.5 SD]（P<0.001）。与方案 A [62.1；52.3]相比，方案 B [55.6；45.8]和方案 C [44.3；39.4]中的信噪比和对比噪声比均显著降低（P<0.05）。与方案 A 和 B 以及方案 B 和 C 相比，方案 A 和 B 之间的辐射剂量[容积 CT 剂量指数（CTDIvol）：7.1 比 4.7 比 1.4 mGy；剂量长度乘积：199.5 比 132.1 比 39.4 mGy·cm 和 E：3.39 比 2.25 比 0.6 mSv]显著降低（P<0.05）。
本动物研究证明了在不显著降低诊断准确性的情况下，使用 120 kV 时 80 mAs 有效剂量的低剂量 CTPA 方案可用于 PE 评估。使用“超低”剂量 CTPA 方案（80 kV；80 mAs 有效剂量）时，段和亚段水平的栓塞物检出率显著降低，而中央栓塞物的评估仍具有较高的诊断准确性。
